One point is They controlled between 60 and 90 percent of the U.S. trade in African slaves.
I posted the article in response to this claim:
“Most slave traders weren’t “Yankees” but British, Dutch, Spanish, Portuguese, or French, and most of the slaves who came to the 13 colonies or the United States came on their ships.”
The article maintains that the Rhode Island/ New England traders controlled 60-90% of the American slave trade.